Conventionally, for example, as disclosed in Japanese Laid-Open Patent Application 4-121260, a brake force control apparatus which generates, when an emergency braking is required, a brake force greater than that generated in a normal time is known. The above-mentioned conventional apparatus comprises a control circuit which generates a drive signal corresponding to an operational speed of a brake pedal and a fluid pressure generating mechanism which generates a brake fluid pressure corresponding to the drive signal generated by the control circuit.
The control circuit determines that, when an operational speed of a brake pedal is less than a predetermined value, the brake pedal is not normally operated. In this case, the fluid pressure generating mechanism is controlled so that a brake fluid pressure corresponding to a brake pressing force is generated. Hereinafter, this control is referred to as a normal control. Additionally, the control circuit determines that, when an operational force of the brake pedal exceeds a predetermined value, an emergency braking is required by the driver. In this case, the fluid pressure generating mechanism is controlled so that a brake fluid pressure is maximized. Hereinafter, this control is referred to as a brake assist control. Thus, according to the above-mentioned conventional apparatus, a brake force corresponding to a brake pressing force can be generated in a normal time, and a large brake force can be immediately generated in an emergency.
Conventionally, in order to prevent a lock of a wheel during a braking operation, an antilock brake control (hereinafter, referred to as an ABS control) is applied to a brake apparatus of a vehicle. The ABS control is for preventing a lock of a wheel by changing a state of a brake force among three states, that is, a pressure-increasing state, a holding state and a pressure-decreasing state so that a slip rate of the wheel does not exceed a predetermined value. Accordingly, when performing the ABS control, a brake force is intermittently changed in association with the changeover among the above-mentioned three states. Thus, when the ABS control is applied to the above-mentioned brake force, a vibration may be generated in a fluid pressure within the apparatus in association with changes in the brake force. If such a vibration is transmitted to a brake pedal, a movement which is not intended by the driver may occur in the brake pedal. In such a condition, it is determined that an emergency braking is required since an operational speed of the brake pedal exceeds a predetermined value despite that the driver does not perform an emergency braking operation, and the brake assist control may be started which results in an incongruous feel provided to the driver. Accordingly, in the above-mentioned conventional apparatus, the brake assist control may be improperly performed due to a vibration in a fluid pressure generated during an execution of the ABS control even when an emergency braking is not required, and, thereby, a riding quality of the vehicle may be deteriorated.